One purpose of the fractional-dedicated physical channel (F-DPCH), which was introduced in Release 6 of the 3GPP UMTS Standard (Rel 6), is to reduce the amount of downlink (DL) channelization codes used for dedicated channels. Instead of allocating one dedicated physical channel (DPCH) for the sole purpose of transmitting one power control command per slot, the F-DPCH allows up to ten wireless devices (also referred to as user equipment (UEs)) to share a single channelization code for this purpose. The F-DPCH uses a spreading factor of 256 and quadrature phase shift keying (QPSK) modulation.
FIG. 1 illustrates an example F-DPCH frame structure. The frame structure of the F-DPCH is straightforward. Each frame 5 of length 10 ms is split into 15 slots 10, where each slot consists of 2560 chips. Each slot 10 contains 10 symbols where each symbol consists of 2 channel bits. Every symbol corresponds to one transmit power control (TPC) command; bit sequence 11 represents TPC command UP and bit sequence 00 represents TPC command DOWN. Consequently, every slot 10 can carry up to 10 TPC commands and hence one F-DPCH can accommodate up to 10 wireless devices.
In the specifications, wireless devices are allocated different TPC command symbols to listen to by assigning the wireless device a certain F-DPCH channelization code, a F-DPCH frame timing, and F-DPCH slot format to listen to. The concept is illustrated by FIG. 1 and Table 1 below.
TABLE 1F-DPCH fieldsChannelSlotChannelSymbolNTPCFormatBit RateRateBits/NOFF1Bits/NOFF2#i(kbps)(ksps)SFSlotBits/SlotSlotBits/Slot031.5256202216131.5256204214231.5256206212331.5256208210431.5256201028531.5256201226631.5256201424731.5256201622831.5256201820931.5256200218
The F-DPCH frame timing may be different for different F-DPCHs, but the offset from the primary common control physical channel (P-CCPCH) frame timing is a multiple of 256 chips (i.e., τF-DPCH,p=Tp×256 chip, Tp∈{0, 1, . . . , 149}). All F-DPCHs transmitted to a wireless device (i.e., UE) from the same high speed DL shared channel (HS-DSCH) cell set have the same timing.
FIG. 2 illustrates an example F-DPCH timing scheme for multiple wireless devices. As shown in FIG. 2, the radio network controller (RNC) can configure combinations of F-DPCH frame timing and F-DPCH slot formats to ensure that multiple wireless devices (i.e., UEs) are allocated different TPC symbols to use on the same F-DPCH channelization code. Specifically, FIG. 2 depicts three example combinations of F-DPCH frame timing and F-DPCH slot formats. Example combination 20 for UE1 has a frame timing of τF-DPCH=0×256 chip and slot format #1. Example combination 22 for UE2 has a frame timing of τF-DPCH=3×256 chip and slot format #1. Example combination 24 for UE3 has a frame timing of τF-DPCH=0×256 chip and slot format #2. Thus, it can be seen from FIG. 2 that two wireless devices (i.e., UE1 and UE2) will have non-overlapping TPC commands even though they both use slot format #1, and UE1 and UE3 will have non-overlapping TPC commands even though they use the same F-DPCH frame timing.
Instead of referring to the combination of F-DPCH frame timing and F-DPCH slot format, the concept of an F-DPCH TPC symbol position may be simplified and defined. For example, there are 10 different such symbol positions, corresponding to TPC symbols transmitted every slot, with an offset from the P-CCPCH slot boundaries of k*256 chips, where k corresponds to the symbol position number and k=0, 1, . . . , 9. Hence, in the above example in FIG. 2, the F-DPCH TPC symbol positions are 2/5/3 for UE1/UE2/UE3 (example combinations 20, 22, and 24, respectively).
A wireless device (i.e., UE) is exclusively assigned a particular F-DPCH TPC symbol position on a specific F-DPCH channelization code. Two wireless devices cannot share the same symbol position on the same channelization code.
An F-DPCH carries control information generated at layer 1 (e.g., TPC commands) for one uplink (UL) dedicated physical control channel (DPCCH) associated with the F-DPCH by higher layer signaling. If dedicated physical control channel 2 (DPCCH2) is configured, an additional F-DPCH carries control information generated at layer 1 (e.g., TPC commands) for one UL DPCCH2 associated with the F-DPCH by higher layer signaling. If DPCCH2 is configured, the slot format of F-DPCH associated with the DPCCH is different from the slot format of F-DPCH associated with the DPCCH2.
In compressed frames, F-DPCH is not transmitted in DL transmission gaps given by transmission gap pattern sequences signaled by higher layers.
Approaches to reduce the TPC frequency and hence energy spent on transmitting TPC bits on F-DPCH have been proposed. One proposed approach employs discontinuous transmission (DTX) of TPC commands to reduce the control frequency. Hence, the TPC command is only transmitted in 1 out of N consecutive slots, while the other TPC commands are DTXed in the remaining N−1 slots. When the wireless device receives the transmitted TPC command, it can adjust its transmitted power accordingly, but due to the DTX, it will only apply an inner loop power control change every N slots.
FIG. 3 illustrates example TPC command transmissions on the F-DPCH. More particularly, FIG. 3 illustrates examples of how TPC commands are transmitted to one wireless device on the F-DPCH. FIG. 3 illustrates three example scenarios 30, 32, and 34. Example scenarios 32 and 34 (the two reduced frequency examples (500 Hz, N=3)) show different TPC timings depending on whether it is the first or last TPC command of the N consecutive TPC commands that shall be transmitted.
In the future, 3GPP may standardize a reduced TPC frequency solution where the last of the TPC commands in a group of N commands will actually be transmitted, where the first slot of the first group corresponds to the first slot in the F-DPCH frame. This is because the reduced power control frequency algorithm can be seen as a variant of the already specified “Algorithm 2.” As stated in 3GPP TS 25.214, V12.2.0 (2015-03), section 5.1.2.2.3.1, “the UE shall process received TPC commands on a 5-slot cycle, where the sets of 5 slots shall be aligned to the frame boundaries and there shall be no overlap between each set of 5 slots.”
Alternatively, 3GPP may standardize a solution where the first TPC command in the group is transmitted. In the study item 3GPP TR 25.706 V2.0.0 (2015-06), section 5.1.1.3, it is suggested to send the first TPC command in the group. Specifically, “the solution of reduced TPC frequency with DTX of TPC commands is proposed so that the TPC command is only transmitted at the first slot in every N consecutive slots, and the other TPC commands are DTXed in the remaining N−1 slots. UE can respond to the first TPC command.” In any case, in 3GPP there has only been discussion on “hard-coding” which slot (out of the N slots comprising a cycle) should convey the TPC command.
In compressed frames, Transmission Gap Length (TGL) slots from Nfirst to Nlast are not used for transmission of data. The particular frames that are compressed are decided by the network. When in compressed mode, compressed frames can occur periodically, or requested on demand. There is only one type of frame structure defined for DL F-DPCH compressed frames: transmission is turned off during the whole transmission gap (i.e., in slots Nfirst to Nlast). The maximum idle length is defined to be 7 slots per one 10 ms frame.
FIG. 4 illustrates example transmission schemes for single and double frame methods for transmission of radio frames. More particularly, FIG. 4 illustrates an example of a single-frame method for transmission of radio frames 42 and an example of a double-frame method for transmission of radio frames 44. As depicted in FIG. 4, transmission gaps 46 may be placed at different positions as appropriate for the individual purposes of inter-frequency power measurement, acquisition of control channel of other system/carrier, and actual handover operation.
The restrictions described below apply to DPCCH/DPCCH2/S-DPCCH/DPDCH in the UL and DPCH or F-DPCH in the DL.
When using the single-frame method as shown in example 42, transmission gap 46 may be located within the compressed frame depending on the TGL. When using the double-frame method as shown in example 44, transmission gap 46 is located on the center of two connected frames.
Parameters of the transmission gap positions may be calculated as follows:                TGL may be the number of consecutive idle slots during the compressed mode transmission gap. Thus,                    TGL=3, 4, 5, 7, 10, 14.                        Nfirst may represent the starting slot of the consecutive idle slots. Thus,                    Nfirst=0, 1, 2, 3, . . . , 14.                        Nlast shows the number of the final idle slot and is calculated as follows:                    If Nfirst+TGL≤15, then Nlast=Nfirst+TGL−1 (in the same frame),            If Nfirst+TGL>15, then Nlast=(Nfirst+TGL−1) mod 15 (in the next frame)When transmission gap 46 spans two consecutive radio frames, as in example 44, Nfirst and TGL must be chosen so that at least 8 slots in each radio frame are transmitted.                        
In the discussion around the proposed solution of reduced power control frequency, the opportunity to let several wireless devices share the same F-DPCH TPC symbol position and channelization code, and thereby allow more than 10 UEs to fit onto the same F-DPCH code, has not been discussed. In addition, there may be negative performance impact in compressed mode from the reduced power control frequency, since not only is there no transmission of power control command during a transmission gap 46, there can also be N−1 slots before and N−1 slots after the transmission gaps where UL power control is not active (no TPC sent on F-DPCH).
In addition to the generation of TPC commands sent by the network node for controlling the UE's transmit power, another important consideration is the generation and handling of TPC commands sent by the UE for controlling the network node's transmit power. The changes that result from reduced TPC frequency operation have an impact on the generation and handling of TPC commands sent by the UE for controlling the transmit power of the network node. When the N-slot “DTX of TPC commands” algorithm is utilized there are N−1 slots in which the UE will not have any information (i.e., a Signal-to-Interference Ratio (SIR) estimate) to derive TPC commands. Also, when the algorithm “Repetition of TPC commands” is used, it is unclear if SIR estimation used to generate TPC commands should be performed on the combined symbols, or on each symbol.